Electronic control units are used in a wide variety of technical fields. One important application is the field of automotive engineering. Since electronic control units in motor vehicles are exposed to harsh environmental conditions, such as high temperatures, strong vibrations, etc., and because motor vehicles usually offer very little room for installing electronic control units, arranging individual circuit components on essentially known p.c. boards, while designing other circuit components as hybrids has been known for some time. These types of hybrids are arranged on the p.c. board and attached to the circuit components of the p.c. board with electrically conductive connections.
German Published Patent Application No. 196 27 663, for example, describes an electronic circuit which is composed of a main board and secondary boards that have different coefficients of thermal expansion and are attached to one another.
These types of electronic circuits and control units have a great advantage in that circuit components which are very sensitive to environmental influences, for example temperature- and vibration-sensitive circuit components such as microcontrollers, processors and the like, can be designed as hybrid circuits, while circuit components that are less sensitive to environmental influences can be implemented as p.c. board circuits in the known manner. Combining the hybrid and p.c. board technologies offers the further advantage that circuit components which can be used simultaneously in several different electronic control units and circuits can be designed as hybrid circuits, with individual circuit components being implemented as p.c. board circuits. This makes it possible to produce a great variety of circuits which meet strict environmental requirements while simultaneously keeping production costs low.
However, heat dissipation from hybrids mounted on p.c. boards frequently presents a problem.